Collimating sight and reflecting aiming post for indirect aiming of a gun



1949 L. H. BROWN 2,491,476

COLLIMATING SIGHT AND REFLECTING AIMING POST FOR INDIRECT AIMING OF GUNS Filed June 9, 1944 2 Sheets-Sheet 1 Ill- /00 Dec. 20, 1949 Filed June 9, 1944 L. H. BROWN COLLIMATING SIGHT AND REFLECTING AIMING' POST FOR INDIRECT AIMING OF GUNS 2 Sheets-Sheet 2 l Ill 11/ Ill; HM 1 git 0W LED I-LERDWN,

MW /Mm W Patented Dec. 20, 1949 UNITED STAT ENT if.

COLLIll/IATING SIGHT AND REFLECTING AIMING POST FOR INDIRECT AIMING OFAGUN (Granted under the act of March 3, 1883, as amended April 30, 1928; 370 0. G. 757) 2 Claims.

The invention described herein may be manufactured and used by or for the Government for governmental purposes, Without the payment to me of any royalty thereon.

This invention relates to fire-control method and apparatus for cannon of all types, particularly mortars, and howitzers.

One form of cannon, namely a mortar, in particular a trench mortar, is referred to hereinafter to explain the application and utility of the invention, although it is to be understood that the invention may be used in indirect firing or indirect laying of other kinds of cannon or means for projecting missiles or projectiles. The invention is particularly useful in connection with controlling the fire of cannon Whose projectiles have comparatively low muzzle velocities and which are fired with their bore axes at comparatively large angular elevation above the horizontal, examples of which are mortars of all types and howitzers.

For the purpose of explaining and describing the application and utility of the invention, a particular form of sighting means for sighting on a particular point or on an aiming post has been selected, namely a collimator sight. It is to be understood, however, that any other suitable sighting means for establishing a line of sight may be used instead of a collimator sight, as for example a telescopic sight having a reticle which preferably may be illuminated in any suitable manner.

An object of the invention is to provide improved method and means for setting or adjusting the azimuth of cannon in indirect firing or indirect laying. In indirect firing the target is not visible from the cannon and the regulation or adjustment of the azimuth or traverse and the elevation of the cannon is made in accordance with data or instructions received from an observer who is situated at a point or location from which the efiect of the fire, the hits or misses,

can be observed. This observer, observing the misses, gives the necessary instructions or data to the gun crew with regard to change of azimuth or change of elevation, or change of both.

The present invention is particularly concerned with method and means for setting the azimuth of the cannon in accordance with data received from the observer mentioned above.

According to the present practice of indirect firing, an aiming post, consisting essentially of a rod planted vertically in the ground, is placed at a distance from a cannon, and a sighting device, e. g., a collimator sight or telescopic sight,

carried on a part of the cannon which traverses with the barrel is sighted on the post or a mark or light on the post. If now, for example, after a projectile has been fired, the observer reports that the azimuth of the cannon should be changed, let us say, X mils to the right, the sight is moved or rotated X mils in azimuth to the left of the aiming post, While the traversing means of the cannon remains fixed. Then the traversing means of the cannon is operated so as to traverse the cannon with the sight to the right until the aiming post is again in the line of sight of the collimator sight or telescopic sight. It will, therefore, be seen that these operations traverse the mortar or howitzer X mils to the right. In night firing, a small electric light bulb energized by a dry cell or cells, is attached to the aiming post, and serves as the point of the post on which the collimator sight or telescopic sight is sighted.

From the foregoing it will be evident, that two factors may introduce errors. These factors are: (l) the whole cannon may move backward, i. e., further away from the aiming post, under the influence of the recoil in firing, and (2) the whole cannon may also move laterally under the same influence. Either of these movements will cause the line of sight of the collimator to be no longer on the aiming post, except in the case where theline of backward movement of the mortar or howitzer happens to be parallel with the line of sight of the collimator or telescopic sight. Therefore, if a correction of Y mils is now directed or indicated by the observer, and applied to the sight as above explained, the correction applied will be in error by an amount depending upon how much laterally and how far backwardly the cannon has moved. Where the aiming post is located at a large distance from the cannon, these errors are usually ignored, particularly after the cannon has become set in the ground after several firings. However, where the aiming post is at a short distance from the cannon, these errors become material and cannot be ignored when strict accuracy is to be maintained.

Lateral thrust or lateral movement of the cannon also is a material factor in indirect firing, even when the aiming point or aiming post is at a comparatively large distance from the piece, where the cosine of the angle between line of fire and the transverse axis of the whole artillery piece is large since then there would be a large or considerable component of the recoil laterally or parallel with the transverse axis of the piece. This component tends to produce lateral displacement of the cannon, and where large, may introduce errors if the aiming point or aiming post is not sufiiciently removed from the cannon. Thus, even with a large distance between the aiming post and the; cannon, the, error due to lateral displacement. of the piece may not be negligible in adjusting or setting the azimuth of the cannon barrel.

From the foregoing it will be seen that in indirect firing or indirect laying; of cannon as heretofore practiced, it is essential in the interest of accuracy to place the aiming post or point at a considerable distance from the, cannon or sight, e. g., collimator sight, carried thereby. This distance is usually of the order ofmagnitude of fifty yards. The positioning of the aiming post under conditions of combat ma be hazardous, and hence it is desirable to avoid exposure of personnel to this hazard during the time required for personnel to place the post in position and:to.removeitafter'firing at the particular location; has been: completed. The present. invention eliminates this hazard, since it permits. the aiming post tobe placed at a few feet orat a few yardsLfrom the cannon without the introduction. of-J errors in sighting due to lateral. displacement or backwardv displacement of: the ca'nnonl Thus; according to the present invention, the aiming post maybe placed a few feetor-a few yards fromthe cannon in the same pit or.- trench in-which the cannon, e. g., mortar orhowitzer, is-l'ocated or; behind the same cover which shields the cannon and the personnel serving it.

The present invention-therefore has among its objects the elimination of errorsdue to backward or lateral movem'ent of: the cannon in the azimuthal control or setting in indirect firing thereof:

Still another object of the present invention consists in the/provision of an aiming post which can be located-- at very: short distances from cannon; such as mortars:- and" howitzers, while nevertheless permitting accurate control of indirect fire or indirect laying of the piece.-

The method of setting'the'azimuth ofa cannon accordingto-the-present invention comprises a number ofsteps oroperations;

The first step ofthe'm'ethod consists" in estab lishingafixed plane light reflecting specular-- suriaceor mirror having considerablelateralextentor horizontal dimension; at a position re moved' from the' cannon-or sighting means carried-by-it inits-traverse. This plane specular light-reflecting means may consist of a lonenarrowmirror; the length -or horizontal dimension' of which may; me'x'ample, be from one foot to three feet in length, depending on the lateral 'displacement'of the cannon, also referred to hereinafter. Th'eplane' light reflecting surface may be constituted bytwo. such plane narrow mirrors arrangedatairight angleto each other wither-longer dim'ensionof each at the vertexiof the right ,angle orthe plane light reflecting-surface'may be'; constituted by a long right angle triangular, prism,-, for example, about one foot to eighteenwinches inlength; and silvered'or otherwisecoated-wlth a specular material on the" faceswhich intersect to form-the rightaangle'; The: long: dimension of said fixed; light arefiecting... surfaces isrhorizontally disposed above th'e surfacepfcthe-nground in'a fixed or: stationary position .at :a" distance: from the cannon;

The second step of the method consists in establishing a line of sight perpendicular to the lateral extent or direction, i. e., to the horizontal length or dimension, of the said plane light refleeting, surfaces. This. may be donev by placing the line of sight" of a collimator in a position to cause the image of the reticle thereof to coincide with or overlap the image produced by said plane light reflecting means of a light emitting or light reflecting fiducial line or point carried in traverse". with the collimator sight. This fiducial line or point, generally referred to herein as a. fiducial indicium, is preferably placed in the vertical plane containing the line of sight of the collimator'sight, although it ma be placed near to such plane without introducing appreciable error. The said fiducial indicium is placed in" the said vertical plane preferably below the line of sight of the collimator sight. It may be placed immediately below the reticle end of a collimator sight in the vertical plane containing the-line of sight, 0'1" optical'axis, of thecollimator sight. It. will be understood, therefore, that when the image of the reticle'of the collimator sight is superimposed upon the image of the fiducial indicium, the line of sight of. the 001- limator sight is perpendicular to the lateral direction or horizontal: dimension of the plane light reflecting surfac'er Now even though the:

cannon moves backward in recoil or moves laterally the lineofsight ofr the'collimator remains:

perpendicular to the longitudinal direction of the reflecting surface, regardless whether the direction of recoil is perpendicular: to; the longitudinal' direction of the refiecting'surface. Even though the whole cannon. may turn in firing about a vertical'axis, errors in sighting are not introduced-thereby.

The thirdastep. of'the'. method consists in applyingto theazimuthal-reading of the collimator sight the correctional data directed by the observer and then traversing the cannon with the collimator'sight until thedmageof the reticle of the collimator sight and .the' image ofthe fiducial indicium'are superimposed one upon the other. For example, l'et it besupposed that the observer instructs that the'fire be-directed Z mils further' totheright. Even if the cannon has moved backward orlaterally or both," itis only necessary to change the setting of the'coll imator sight Z mils to-tlie left, and'then traverse the cannon together with the collimator sight until the image of the mils)" to the-left and the-correction of Z mils tothe right -'of the previous position is desired. Obviously; traversing the cannon backto the positionwh'ere'the image of the-reticle of the collimatorsight'and-the image -of'the fiducial indicium overlap will traverse the cannon the said V mils to' the right, and the azimuth of the cannon will be the sameas-it was 'beforei- Now the correctional dataof -Z- mils to the'right maybe applied by rotatingthe' sight Z'mils tothe left and again traversing the cannon to the-right until the image of the collimator reticle and the-image of the fiducial' indicium" overlap or come into the desired relative position; From this explanation, it

'mzis sintroducedxintothercoll-imator sight azimuth reading by rotating it Z mils to the left, and then the cannon traversed to-the right until the image of the collimator sight reticle and the image of the fiducial indicium overlap, the cannon in one traversing operation is traversed Z mils to the right of its previous firing position.

As was mentioned above, a telescopic or other sighting means for establishing a line of sight may replace the collimator sight referred to above. Where a telescopic sight is used, the reticle in the telescopic sight, whether or not illuminated, serves the same purpose and is used in the same manner as the reticle of the collimator sight.

From the foregoing explanations, it will appear that that dimension of the light reflecting specular surface or surfaces disposed in a horizontal direction is greater than the component of the lateral or sidewise displacement of the cannon along a direction parallel to the plane of the specular light reflecting surfaces or mirrors, since otherwise it would be impossible to dispose the parts of the fire control means so that the line of sight of the collimator sight or other sighting means, after said displacement, meets the said longitudinal dimension perpendicularly. In the absence of said meeting, no image of the fiducial indicium in the vertical plane of the line of sight would be visible.

Referring now in detail to the accompanying drawings illustrating several embodiments of apparatus comprising the invention and suitable for use in practicing the method of the invention,

Fig. 1 is a side elevation, partly in vertical section, of a known collimator sight; and an aiming post constructed according to the present invention, and illustrating how the two co-operate in sighting.

Fig. 2 is a rear elevation, partly in section, of the collimator sight shown in Fig. 1, but on a smaller scale, and also illustrating how the collimator sight may be attached to a part of a mortar that is traversed with the barrel of the mortar.

Fig. 3 is a side elevation of an aiming post, constructed according to the present invention, embodying two long narrow plane mirrors at right angles.

Fig. 4 is a perspective view of another embodiment of the aiming post of the present invention in which a single long plane narrow mirror is employed.

Fig. 5 is a front elevation of another aiming post constructed according to the present inventicn in which two plane mirror surfaces at right angles, provided by a long triangular prism, silvered on the faces perpendicular to each other, are employed.

7 Fig. 6 is a top plan of Fig. 5.

Fig. 7 is a cross section on the line I-1 of Fig. 5, showing the triangular prism in section.

Fig. 8 is a perspective view showing the parts of the aiming post illustrated in Figures 5, 6 and 7 assembled together for transport or storage.

Fig. 9 is a perspective view of an illuminating means which may be placed over the reticle end of the collimator sight, and containing an electric light bulb for illuminating, when necessary, the reticle of the collimator sight and the fiducial indicium on the said sight.

Fig. 10 is a side elevation of part of the collimator sight showing the illuminating means shown in Fig. 9 applied thereto.

Fig. 11 is a cross section on the line ll-H of, Fig. 10.

In Figures 1 and 2 there is shown a known collimator sight 1, which may be transversed and moved in elevation by rotating graduated heads 2 and 3 respectively. Heads 2 and 3 are graduated in mils or degrees as desired. The collimator 4, comprising the usual collimating lens 5 and reticle plate 6, is carried on a head 1. Head 1 is carried on a bolt 3 and fixed for rotation therewith. Bolt 8 passes with a sliding and rotating fit through a hole in the standard 9 of the plate In which is traversed by rotating the head 2. This construction enables the collimator 4 to be adjusted in elevation independently of elevating head 3.

According to the present invention fiducial lines or points are placed on the collimator sight, preferably as explained above, below the reticle on reticle plate 6 and in, or substantially in, the vertical plane containing the line of sight of the collimator sight. Such a fiducial line is indicated in Fig. 1 by the numerals I5 and [6, which indicate the extremities of the line. This line may 4 be a narrow white line, or line of other color, and

whose image in a plane mirror is easily visible.-

The collimator sight I is removably mounted on a part I? of a mortar which traverses with the barrel when the traversing means of the mortar are operated. This mounting is provided by a bracket H) of the collimator sight which engages within a slot [9 in the traversing part 11. The collimator sight i carries a latch 23 having a catch 2! which engages beneath a shoulder 22, for the purpose of releasably holding the collimator sight on the said part I1.

Across level 23 and a longitudinal level 24 are carried by the collimator sight I and are used to place the plane of traverse of the collimator horizontally. When angles of azimuth are referred to herein, it is of course understood that they are measured in a horizontal plane. When, therefore, the sight is adjusted level according to the two levels 23 and 24, the plate is carrying the collimator moves in a horizontal plane when the collimator d is traversed by rotating the knobor head 2.

Referring now to the modification of the aiming post illustrated in Figs. 1 and 3, there is shown a post 25 which may be planted vertically in the ground at a position removed from the mortar. On the post is mounted a U-shaped bracket 26. The post 25 passes through openings in the two arms 21 and 28 of the bracket, and the bracket may be secured in any desired position along the length of the post by means of butter-fly screws 29 and 30 which fit threaded openings in the bracket. Turning the screws 29 and 30 until they tightly engage the post 25 fixes the bracket 26 in position on the post.

Two long narrow mirrors 3| and 32 are mounted, at right angles to each other, in a long V-shaped trough-like member 33. The edges 34 and 35 of this trough-like member may be turned over the edges of the mirrors, as shown in Figs. 1 and 3, to protect said edges of the mirrors.

The two bracket arms 2'! and 28 have tongues 36 and 31 punched from them, and between these tongues and the inwardly bent ends 38 and 39 of the bracket arms 21 and 28 is held the trough-like member carrying the long narrow mirrors 3| and 32.

The aiming post or means illustrated in Fig. 4, and constituting another modification of an aiming means constructed according to the invention,

7 comprises a post -45'having a four bladed spear head 46 at the bottom end to enable the post-to be easily planted vertically in the ground and to hinder or prevent rotation of the post after itis planted in verticalposition at'a point removed from the mortar. This modification of the aiming post is also provided with a bracket 41 that is in all respects similar to bra'cket'26 disclosed Fig. 3. In the bracket 4'! is mounted a long'narrow channel member 48 with edges 49 and B bent two pointed posts 60 and iii, of like construction,

two clamps 62 of like construction and along channel member 64 in which a long right angle triangular glass'or plastic prism 65 is mounted lengthwise of the channel member.

The faces 66 and 61 of the prism 65 meet at an angle of ninety degrees, and are silvered, whereby two plane mirrors at an angle of ninety degrees are obtained.

Channel member 64 is provided with inwardly bent marginal portions 68 and 69, between which and the bottom of the channel member the prism 65 is mounted. The face II of the prism is so disposed that it is parallel with the bottom 10 of channel member 64. The prism is mounted in channel member 64 on a rubber carrier 12 to which it may be cemented, and resilient packing such as sponge rubber, wool or kapok I3 is packed between the rubber carrier 12 and the bottom III of channel member 64.

Each of the clamps 62 comprises a back portion 80provlded with a thumb screw M which fits and passes through a correspondingly threaded hole in back portion 80. Four fingers -82 extend from back portion 80 in a manner clearly shown in Figs. '5, 6, 7 and 8. free end is provided with an inwardly bent tip "83.

When the modification of the aiming post'or surface illustrated in Figs; 5, 6, '7 and 8 is in use, the various parts are assembled'as shown in Figs.

5,6 and 7. However, when it is desired to trans-- port or store the parts, they are advantageously assembled as shown in Fig.8.

musing all of the modifications oi the aiming posts herein described, the long dimension of the mirrors is disposed substantially horizontal with f reference to the earth.

The illuminating means'for illuminatingwvhen necessary, the reticle of the collimator sight and the fiducial indicium is shown in Figs-9, 10 and 11. This illuminating means comprises a substantially cubical box 96 consisting of top portion 9I, bottom portion 62, end portion 93 and side portions 64 and 95. The side portions 94 and'95 extend rearwardly of the cubical portion and then downwardly, as shown in Fig. 9, in order to form two spaced wings adapted to fit and slide over the end of collimator 4 and head 1 of the collimator sight, as shown inFigs. lO'and 1-1. A small electriclight bulb 96 is located in the cubical box 96 and is carried in a socket 91;

Each of the "fingers 82 at its I the box 90.

G of collimator '4. The illuminating means is held on the sight in the position illustrated in Figs. 10 and 11 by means of a thumb screw 99 threaded in the wing portion of the side 95 of Turning'this screw into tight engagement with the head "i of the sight clamps the illuminating means to the sight. The illuminating means isused when ordinary solar light is not surlicient'to renderthe image of the collimator reticle and the image of the fiducial indicium clearly visible.

The use of two plane mirrors at'an angle of ninety degrees to each other, as show-n in Figs. 1. 3, and 7, has the advantage that any light ray in a plane normal to said plane mirrors and incident atany angle on either-of them, and which causes deflection of the ray to the other 'of said mirror, is reflected from the other of said mirrors in a path which is parallel to the path of the said ray. This-condition is clearly illustrated in Fig. 1, whichillustrates the use of the invention but with the mirrors -3l and 32 shown much nearer to the collimator sight I than they would be in actual use. In this figure the eye of the user in sighting is indicated by the numeral I66. A light ray I proceeding from point I5 of the iiducial line is refiected'bythe two mirrors as ray I i5 which is parallel to ray I05. Similarly a light ray I96 proceeding frompoint I6 of the fiducial line is reflected by the twomirrors as ray H6 whichis parallel to ray I06.

Rays I I5 and H6-enter the'eyelllllof the user who simultaneously seeks to view the image of the fiducial line and the image of the reticle of the collimator 4, and tosuperimpose them.

The manner of use of the apparatus for practicing is clear from the preceding disclosures. However, in conclusion, an illustrative example of use of the invention is given. Let it be'supposed that the aiming post of the invention illustrated in Figs. 1 andS is located in the second quadrant about midway between and Themortar is layed according to the firing data and then thecollimatorsight is adjusted by turning knob or head 2 until the eye 166 of the user sees the imag .of the reticle of the collimator sight I overlapping or superimposed upon the image'of the 'fiducial line I5, I6 produced by mirrors 3I and 32. The line of sight ofthe collimator 4, or the vertical plane containing it, is now perpendicular to the horizontal dimension of the mirrors 31 and 32, and in a plane normal to both of the surfaces of the said mirrors.

The mortar is now fired. The observer spots the shot. and'advises the mortar crew how many mils the azimuth of fire should'be changed. Let it *be supposed that the observer directs that the azimuth'be changed Yfive mils to the right. The knob or head 2 is then turned so as to traverse the collimator 4 five mils to the left, after which the traversing means of the mortar is actuated to traverse the mortar to the right, together with the whole collimator sight -I attached to part I! which traverses with. the mortar, until the eye I06 of the user again sees the image. of the reticle of the collimator 4 superimposed upon the image of the fiducial-line I.5,.I6; and then the traversing of the mortar is discontinued. The mortar then has been traversed five mils to the right in accordance with the directions of the observer.

I claim:

1. For use in the indirect aiming of a gun mounted for elevation about a normally hori-- zontal axis upon apart trainabl about a vnormally vertical axis, the combination with said gun, of a collimating sight mounted upon said part for movement therewith and angular movement relatively thereto about normally vertical and horizontal axes, a sighting mark on said sight in the same vertical plane as the reticle of said sight, an elongated plane reflector, and means mounting said reflector adjacent and independently of said gun remote from the vertical plane through the bore axis of said gun, said reflector being mounted with its elongated dimension substantially horizontal and all lines of its specular surface parallel to said dimension perpendicular to a line between said mirror and sight, to thereby reflect an image of said sighting mark into alignment with said reticle.

2. For use in the indirect aiming of a gun mounted for elevation about a normally horizontal axis upon a part trainable about a normally vertical axis, the combination with said gun, of a collimating sight mounted upon said part for movement therewith and angular movement relatively thereto about normally vertical and horizontal axes, a sighting mark on said sight in the same vertical plane as the reticle of said sight, an elongated plane mirror, and means mounting said mirror adjacent and independently of said gun remote from the plane of fire, with its longitudinal axis horizontal and its reflecting 10 surface perpendicular to a line between said mirror and sight, to reflect an image of said sighting mark into alignment with said reticle. LEO H. BROWN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 377,908 Phillips Feb. 14, 1888 527,640 Wetherill Oct. 16, 1894 1,377,161 Vanderbeck May 3, 1921 1,384,014 Fessenden July 5, 1921 1,699,926 Seume Jan. 22, 1929 1,723,456 Zak Aug. 6, 1929 2,239,469 Reason Apr. 22, 1941 2,380,501 Christian et al July 31, 1945 FOREIGN PATENTS Number Country Date 2,510 Great Britain 1908 17,181 Great Britain 1901 17,371 Great Britain 1908 200,683 Great Britain July 19, 1923 240,426 Great Britain Nov. 19, 1925 

